Generate alphabet with 4 copies of each letter

⍪4/⎕A

Matrix format (⍪) of 4-replication (4/) of alphabet (⎕A).

Python - 37

for i in range(104):print chr(i/4+65)

i goes from 0 to 104; it is divided by four and added to the ascii value for A, and the resulting character is printed.

write(rep(LETTERS,e=4),1,1)

Former version with 30 bytes:

cat(rep(LETTERS,e=4),sep="\n")